2D array probes coupled with current generation ultrasound systems are not fast enough to acquire clinically suitable volume sizes for applications such as fetal heart imaging. It is currently not possible to achieve both the required temporal resolution and the required spatial resolution from a single volume acquired with a conventional 2D array probe.
As a result, some conventional ultrasound systems slowly sweep across an entire volume, acquiring a 2D image frames at distinct locations during the sweep. For example, the sweep may take 8-12 seconds for a typical fetal heart. During the time of the sweep, the fetal heart may beat approximately 16 to 30 times. Phase data indicating the cardiac phase at the acquisition of each 2D image frame may be acquired based on data from M-mode acquisitions. According to conventional techniques such as STIC (Spatio-temporal image correlation), images of the entire volume at various cardiac phases are “synthesized” using frames from discrete cardiac cycles. In other words, each volume is not acquired during the same cardiac cycle. Instead, each slice or image of the volume is acquired during a different cardiac cycle. Then, the “synthesized” volumes for each of the cardiac phases may be placed in a sequence representing a complete cardiac cycle. A user may then select to view an image of any plane from within the volume or the user may view a rendering of some or all of the volume.
Conventional techniques like STIC suffer from at least two problems: it takes too long to acquire all of the data; and the resulting volume has limited resolution in a elevation direction. Specifically, since only one 2D image frame is selected from each cardiac cycle, the resolution in the elevation direction is limited to the number of cardiac cycles of the acquisition. Using a technique that requires a long acquisition time also increases the likelihood of acquiring data with motion artifacts. For example, both the clinician holding the 2D array probe and the patient are more likely to move during a longer acquisition. Any relative movement between the 2D array probe and the patient's anatomy being scanned may introduce motion artifacts. Also, any irregularities in a patient's heart movements may result in additional motion or spatial artifacts.
For these and other reasons an improved method and ultrasound imaging system for acquiring 4D ultrasound data is desired.